Flame and shrinkage resistant fabric blends and method for making same

ABSTRACT

Fabric blends of inherently flame resistant fibers and flame resistant cellulosic fibers that contain a flame retardant. According to the method of production of these blends, the inherently flame resistant fibers can be dyed a full shade of color without depleting the flame retardant contained in the cellulosic fibers. In addition, the potential for laundering shrinkage of the inherently flame resistant fibers of the blends is reduced regardless of whether both, one of, or neither of the inherently flame resistant fibers and the flame resistant cellulosic fibers are dyed. Dyeing and/or shrinkage prevention of these blends is conducted at temperatures below 100° C., typically approximately between 70° C. and 100° C. Preferably, dye-assistants used in the process are selected from the group comprising N-cyclohexylpyrrolidone, benzyl alcohol, N,N-dibutylformamide, N,N-diethylbenzamide, hexadecyltrimethyl ammonium salt, N,N-dimethylbenzamide, N,N-diethyl-m-toluamide, N-octylpyrrolidone, aryl ether, an approximately 50/50 blend of N,N-dimethylcaprylamide and N,N-dimethylcapramide, and mixtures thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

Applicant hereby claims priority to and incorporates by reference hereinU.S. patent application Ser. No. 09/610,932 filed Jul. 6, 2000, which isa divsional of U.S. Pat. No. 6,132,476.

FIELD OF THE INVENTION

The present invention relates to flame resistant fabrics. Moreparticularly, the present invention relates to dyed fabric blendscontaining inherently flame resistant fibers and flame resistantcellulosic fibers that contain a flame retardant compound. These dyedfabrics exhibit excellent flame resistance, minimal shrinkage whenlaundered, and can be produced in a full range of colors and shades. Theprocess used to dye the fabric of the present invention effectively dyesthe inherently flame resistant fibers, and simultaneously decreases thereduction in flame resistance of the cellulosic fibers while controllinglaundry shrinkage of the inherently flame resistant fibers.

BACKGROUND OF THE INVENTION

Inherently flame resistant fibers are highly resistant to heatdecomposition and are therefore desirable in the manufacture of flameresistant garments intended for environments in which flames or extremeheat will be encountered. These desirable properties of inherently flameresistant fibers can, however, create difficulties during fabricproduction. For example, fibers composed of aromatic polyamide, commonlyknown as aramid fibers, are difficult to dye. Aramid fiber suppliershave recommended complicated exhaust dyeing procedures with variousdye-assistants, high temperatures, and long dyeing times to effectdyeing of these fibers. Such dyeing conditions require substantialamounts of energy both to maintain the dyeing temperature and for thetreatment of waste dyebaths. Dye-assistants comprised of organic agents,and commonly referred to as carriers or swelling agents, are used toenhance dyeability. Such dye-assistants may be added to the dyebath as atreatment prior to dyeing, or can be integrated into the inherentlyflame resistant fiber during production.

Inherently flame resistant fibers such as aramid fibers can be blendedwith fibers made of other materials. As is known in the art, fiberblending can be used to obtain an end fabric that combines thebeneficial characteristics of each of the constituent fibers. Forinstance, in the area of flame resistant fabric manufacture, flameresistant cellulosic fibers such as flame resistant rayon (“FR rayon”)fibers can be successfully blended with aramid fibers to obtain a flameresistant material which is softer, more moisture absorbent, and lessexpensive to produce than materials constructed only of aramid fibers.

Although improving the texture and lowering the cost of flame resistantfabrics, blending inherently flame resistant fibers with flame resistantcellulosics such as FR rayon can complicate production. Specifically,cellulosics contain flame retardant agents that, although resistant tostandard cellulosic dyeing procedures, tend to be depleted by theextreme temperatures generally considered necessary to dye theinherently flame resistant fibers. This depletion of flame retardantagents significantly reduces the flame resistance of the cellulosicfibers and therefore reduces the flame resistance of these blends.Moreover, these conditions increase the likelihood of further depletionof the flame retardant agents during subsequent launderings and an evengreater reduction in flame resistance.

Due to the danger of depleting the flame retardant agent or agentscontained in the cellulosic fibers of such fabric blends, producers ofcellulosic fibers often advise their customers to avoid dyeing theinherently flame resistant fibers when blended with flame resistantcellulosic fibers. As an alternative, these producers suggest usingproducer colored inherently flame resistant fiber where a colored, flameresistant cellulosic blend is desired. In producer coloring (also knownas “solution dyeing”), pigment or other coloring is typically injectedinto the polymer solution before the fiber is formed. Although providingfor adequate colorization of these fibers, producer coloring presentsseveral disadvantages. First, producer colored fibers usually are moreexpensive than non-producer colored fibers. Second, due to the increaseddifficulty and cost associated with the production of these fibers,typically only a limited variety of producer colored fibers areavailable.

Although dyeing at temperatures below 100° C. substantially reduces thedepletion of flame retardant agents from the cellulosic fibers, such lowtemperature dyeing creates a further complication. Specifically, whenconventional dyeing methods are used at temperatures below 100° C., notonly do the inherently flame resistant fibers resist dyeing, thesefibers become susceptible to substantial laundry shrinkage. Accordingly,if conventional piece-dyeing techniques are employed, the dyer istypically left with a choice between acceptable color and shrinkagecontrol but unacceptable flame resistance on one hand (when dyeing above100° C.), and preserved flame resistance but high laundering shrinkageand poor color yield on the other (when dying below 100° C.). Sinceneither option is commercially attractive, the industry preference forproducer colored inherently flame resistant fibers in such blends isunderstandable.

From the above discussion, it can be appreciated that it would bedesirable to have fabric blends comprising inherently flame resistantfibers and flame resistant cellulosic fibers in which the inherentlyflame resistant fibers have been dyed a full shade of color withoutdepleting the flame retardant agent or agents contained in thecellulosic fiber, while simultaneously reducing the extent to which thefabric will shrink during laundering. Furthermore, it would be desirableto have a method for dyeing such fabric blends to achieve theseproperties.

SUMMARY OF THE INVENTION

The present invention provides fabric blends of inherently flameresistant fibers and flame resistant cellulosic fibers that contain aflame retardant compound. Preferably, both the cellulosic fibers and theinherently flame resistant fibers are dyed without significantlydepleting the flame retardant compound contained in the cellulosicfibers while simultaneously ensuring that the resulting fabric is highlyresistant to subsequent laundering shrinkage.

Although the inherently flame resistant fibers can be composed of anymaterial that is inherently flame resistant, it is preferred that thesefibers are made of an aromatic polyamide, polyamide imide, or polyimide,each of which is recognized in the art as being difficult to dye.Particularly preferred are fibers composed essentially of an aromaticpolyamide such as meta-aramid or para-aramid. Although meta-aramid andpara-aramid fibers share similar characteristics, there are significantdifferences between the two. Notably, meta-aramid fibers have a greatertendency to shrink when subjected to laundering than do para-aramidfibers. Accordingly, dyed meta-aramid blends must be produced in amanner in which subsequent shrinking that typically occurs duringlaundering is prevented or inhibited.

One or more of the above identified inherently flame resistant fibers isblended with one or more types of cellulosic fiber such as rayon,acetate, triacetate, and lyocell. Because these cellulosic fibers arenot naturally resistant to flame, they typically are treated with one ormore flame retardants when flame resistance is required. To prevent theexcessive degradation of these retardants, dyeing is conducted attemperatures below 100° C. Typically, peak temperatures approximatelybetween 70° C. and 100° C. are used, with 85° C. being most preferred.

Dyeing of the inherently flame resistant fibers contained in the fabricblends can be accomplished with one of several dye-assistants. Duringthe dyeing process, the dye-assistant promotes the penetration of theinherently flame resistant fibers by the dye so that the fibers arechanged in color. In that dyeing is conducted at relatively lowtemperatures, dye-assistants that adequately promote dyeing ofinherently flame resistant fibers at low temperatures must be used.Additionally, where shrinkage resistance is desired, the selecteddye-assistant must further limit subsequent shrinkage caused bylaundering. Preferably, this dye-assistant will be selected from thegroup consisting of N-cyclohexylpyrrolidone, benzyl alcohol,N,N-dibutylformamide, N,N-diethylbenzamide, hexadecyltrimethyl ammoniumsalt, N, N-dimethylbenzamide, N,N-diethyl-m-toluamide,N-octylpyrrolidone, aryl ether, Halcomid M-8/10 (an approximately 50/50blend of N,N-dimethylcaprylamide and N,N-dimethylcapramide), andmixtures thereof. Where the greatest shrinkage control is desired, mostpreferred is a dye-assistant selected from the group consisting ofN-cyclohexylpyrrolidone, benzyl alcohol, N,N-dibutylformamide, andmixtures thereof.

In situations in which both the cellulosic and inherently flameresistant fibers of the fabric blend are to be dyed, the cellulosicfibers are first dyed in a conventional manner, such as by exhaustdyeing. After these fibers have been adequately dyed, the inherentlyflame resistant fibers of the fabric can be dyed in the manner describedabove. Normally, the temperature of the dyebath is gradually increasedfrom room temperature to a peak temperature approximately between 70° C.and 100° C. The dyebath is maintained at its peak temperature forapproximately between 30 to 90 minutes to permit the dye to penetratethe inherently flame resistant fibers.

DETAILED DESCRIPTION OF THE INVENTION

As summarized above, the present invention provides fabric blends ofinherently flame resistant fibers and flame resistant cellulosic fibersthat contain a flame retardant compound. Typically, the inherently flameresistant fibers, the flame resistant cellulosic fibers, or both aredyed through an exhaust process. Through the method of the presentinvention, the inherently flame resistant fibers of the fabric can bedyed a full shade of color without significantly depleting the amount offlame retardant compound contained in the cellulosic fibers to preservethe flame resistance of the fabric after the dyeing process is completedand through subsequent laundering. It is to be noted that, for thepurposes of this disclosure, the term full shade denotes penetration ofthe subject fiber with dye and fixation of the dye therein, as opposedto mere superficial staining of the fibers. In addition to flameretardant retention, shrinkage of the inherently flame resistant fibersis reduced through the present method such that the overall fabricshrinkage is within levels considered acceptable by industry standards.

Although the inherently flame resistant fibers can be composed of anymaterial that is inherently flame resistant, it is preferred that thesefibers are composed essentially of an aromatic polyamide, polyamideimide, or polyimide, each of which is considered difficult to dye. Mostpreferably, these fibers will be composed essentially of an aromaticpolyamide. Aromatic polyamides are formed by reactions of aromaticdiacid chlorides with aromatic diamines to produce amide linkages in anamide solvent. Fibers made of aromatic polyamides are generally referredto by the generic term aramid fiber. Aramid fibers are typicallyavailable in two distinct compositions, namely meta-type fibers composedof poly(m-phenylene isophthalamide) commonly referred to as meta-aramidfibers, and para-type fibers composed ofpoly(p-phenyleneterephthalamide) which are commonly referred to aspara-aramid fibers. Meta-aramid fibers are currently available fromDuPont of Wilmington, Del. in several forms under the trademark NOMEX®.For example, NOMEX T-450® is 100% meta-aramid; NOMEX T-455® is a blendof 95% NOMEX® and 5% KEVLAR® (para-aramid); and NOMEX IIIA® (also knownas NOMEX T-462®) is 93% NOMEX®, 5% KEVLAR®, and 2% carbon core nylon. Inaddition, meta-aramid fibers are available under the trademarks CONEX®and APYEIL® which are produced by Teijin and Unitika, respectively.Para-aramid fibers are currently available under the trademarks KEVLAR®,TECHNORA®, and TWARON® from DuPont, Teijin, and Akzo respectively. Inaccordance with the above description, it is to be noted that, in thepresent disclosure, when a material name is followed by the term“fiber,” the fiber described is not limited to fibers composedexclusively of the named material.

Meta-aramid and para-aramid fibers share similar characteristics. Forinstance, both have limiting oxygen indexes (LOI's) approximatelybetween 24 and 30 percent. However, there are significant differencesbetween the two compositions. Notably, para-aramid fibers areconsiderably stronger than meta-aramid fibers, having tenacity valuesapproximately between 21-27 g/d and a tensile strength of about 400 psi.This strength makes para-aramid fibers particularly useful in lawenforcement and military applications. Another significant distinctionbetween meta-aramid and para-aramid fibers is that, although both aredifficult to dye, meta-aramid fibers appear to more readily accept dyeduring the dyeing procedure. Despite being easier to dye, meta-aramidfibers have a greater tendency to shrink when subjected to launderingthan do para-aramid fibers. Accordingly, dyed meta-aramid blends must beproduced in a manner which additionally prevents or inhibits subsequentshrinking due to laundering.

Another group of fibers that have flame resistant properties and thatare difficult to dye are polyamide imides. Sometimes referred to as anaromatic polyamide, polyamide imide is a high performance thermoplasticthat is the condensation polymer of trimellitic anhydride and variousdiamines. Polyamide imide fibers are currently available under thetrademark KERMEL® which is produced by Rhône-Poulenc.

A further group of fibers that have flame resistant properties and thatare difficult to dye are polyimides. Polyimide is chemically known aspoly(4.4′-diphenylmethane-co-tolylenebenzophenonetetracarboxylicimide)and is made by the reaction of benzophenone tetra carboxylic anhydridewith a mixture of tolylene and diphenylmethane diisocyanates in a polaraprotic solvent such as dimethyl-formamide or acetamide. Polyimidefibers are currently available from Lenzing under the trademark P-84°.

In the present invention, one or more of the above identified inherentlyflame resistant fibers is blended with one or more types of cellulosicfiber. Preferred for the choice of cellulosic fibers are rayon, acetate,triacetate, and lyocell. These cellulosics, although softer and lessexpensive than the inherently flame resistant fibers, are not naturallyresistant to flame. To increase the flame resistance of these fibers,they typically are treated with one or more flame retardants such asphosphorus compounds like SANDOLAST 9000°0, currently available fromSandos, antimony compounds, and the like. Generally speaking, cellulosicfibers which contain one or more flame retardants are given thedesignation “FR”. Accordingly, the preferred flame resistant cellulosicfibers are FR rayon, FR acetate, FR triacetate, and FR lyocell.

Of the many blends conceivable with the above described listing ofpreferred fibers, most preferred is a blend of NOMEX IIIA® and FR rayonhaving a percentage composition of NOMEX IIIA® of at least 20% and apercentage composition of FR rayon of at least 10%. Typically, thefabric will comprise a 50/50, 65/35, or a 35/65 blend of NOMEX IIIA® andFR rayon.

The fabric of the present invention can be dyed using customary dyeingequipment. Typically, a dye, a dye-assistant, and a flame retardant forthe inherently flame resistant fibers, are combined to form a mixture,(e.g., a dyebath, solution, dispersion, or the like). The fabric is thencontacted with this mixture, typically by immersion, and the mixtureheated until the dye is fixed in the inherently flame resistant fibers.In accordance with the present invention, a fibrous textile material,e.g., fiber web, web, yarn, thread, sliver, woven fabric, knittedfabric, non-woven fabric, or the like, is placed in the dyebath with thedyes and other additives using conventional equipment such as dye jetsor other appropriate equipment.

The preferred dye-assistants of the present invention are selected fromthe group consisting of N-cyclohexylpyrrolidone, benzyl alcohol,N,N-dibutylformamide, N,N-diethylbenzamide, hexadecyltrimethyl ammoniumsalt, N,N-dimethylbenzamide, N,N-diethyl-m-toluamide,N-octylpyrrolidone, aryl ether, Halcomid M-8/10 (an approximately 50/50blend of N,N-dimethylcaprylamide and N,N-dimethylcapramide), andmixtures thereof. Where the highest degree of shrinkage prevention isdesired, the dye-assistant most preferably is selected from the groupconsisting of N-cyclohexylpyrrolidone, benzyl alcohol,N,N-dibutylformamide, and mixtures thereof.

As an alternative to adding dye-assistant to the dyebath, thedye-assistant can instead be imbibed into the fibers themselves duringproduction. Exemplary of the types of fibers that could be used in thismanner are those disclosed by Vance et al. in U.S. Pat. No. 4,688,234,and Hodge et al. in U.S. Pat. No. 5,074,889, both of which are herebyincorporated by reference. As disclosed by Vance et al., typically asurfactant such as hexadecyltrimethylammonium salt or isopropylammoniumdodecylbenzenesulfonate is added to the fiber at a level ofapproximately 5% to 15% by weight. When the fibers are imbibed withdye-assistant, dyeing is conducted in the same manner as described aboveexcept that no additional dye-assistant need be added to the dyebath.

In addition to the dye-assistants, a flame retardant compound can alsobe included in the dyebath, applied as an after dyeing surfacetreatment, or otherwise incorporated in the fiber to enhance flameresistance or to counteract any deleterious effects of the dye-assistantcontained within the inherently flame resistant fibers. Preferred flameretardants are ANTIBLAZE 80® (“AB80®”) and ANTIBLAZE 100® (“AB100®”)which are both currently available from Albright & Wilson.

Dyes that can be used advantageously with the present carrier for thedyeing of the inherently flame resistant fibers can include anionic,cationic, disperse dyes, and mixtures thereof. Of these dyes,particularly preferred are cationic dyes. With regard to the dyeing ofthe cellulosic fibers, preferred are reactive, vat, and sulfur, withreactive dyes being most preferred.

As described above, dyeing blends of inherently flame resistant fibersand flame resistant cellulosic fibers has, heretofore, been inadvisablebecause the dyeing conditions normally used adversely affect one or bothtypes of the fibers. In particular, the high temperatures conventionallydeemed necessary to attain adequate dyeing and shrinkage control of theinherently flame resistant fibers deplete the flame retardant containedin the cellulosic fibers. Notably, this depletion generally is notremedied by the inclusion of additional flame retardant in the dyebathunder conventional conditions. Furthermore, these conventional dyeingconditions cause increased subsequent depletion of flame retardant whenthe fabric blends are laundered. Under the method of the instantinvention, however, effective dyeing of the inherently flame resistantfibers can be attained at temperatures below approximately 100° C.,without a substantial loss of cellulosic flame retardant and withoutlosing shrinkage control. Typically, temperatures approximately between70° C. and 100° C. are used with approximately 85° C. being mostpreferred. It will be appreciated, however from the data provided below,that temperatures as low as 60° C. and even 50° C. can be used to dyethe blends. However, in that the dyeing process is less efficient andshrinkage prevention more difficult at these lower temperatures, usuallytemperatures between the stated 70° C.-100° C. range are used.

To conduct dyeing of the inherently flame resistant fibers of theblends, a dye-assistant, a dye, and other additives if desired, arepreferably applied to the fibers of the fabric using a one-stepbatch-type process, although split treatment with dye-assistants appliedseparately from the dye is feasible, and in some applications might bedesirable. Typically a roll of fabric is loaded into a jet dyer such asa pressure jet dyeing vessel in which the fabric can be circulatedthrough a apertured venturi contained within the vessel. Once loadedinto the vessel, the ends of the fabric are sewn together to form acontinuous loop. The fabric is then scoured by passing it through anaqueous solution that passes through the apertures in the venturi andimpinges the fabric. After scouring has been completed, the jet is againcharged with water, the selected dye-assistant and dye, and any otherauxiliary additives that are desired. Alternatively, where dye-assistanthas been imbibed into the fibers, no additional dye-assistant is addedto the dyebath since an adequate amount of dye-assistant is typicallyalready contained within the fibers themselves. In such circumstances,the same dye steps apply with the exception of the step of addingdye-assistant to the dyebath.

The temperature of the dyebath is gradually increased from roomtemperature to a peak temperature approximately between 70° C. and 100°C. This gradual increase in temperature is customary in the industry,and is thought to promote even and uniform coloration. Upon reaching thepredetermined peak temperature, the dyebath is maintained at this peaktemperature for about 30 to 90 minutes to allow dye to fully penetratethe fibers. It will be appreciated that since the dyeing temperaturerange does not reach 100° C., there is no need to increase the pressureof the dyebath beyond atmospheric pressure to prevent boiling.Therefore, all dyeing can be conducted at constant ambient atmosphericpressure, although a closed vessel and increased pressure may be used toreduce foaming or control odors.

After the expiration of approximately between 30 to 90 minutes at thepeak temperature, the dyebath is cooled until the fabric is at atemperature at which it can be handled. At this time, the dyebath isdiscarded and the fabric is again scoured to remove excess dye-assistantor other chemicals contained in the inherently flame resistant fibers.After all dyeing has been completed, the fabric then can be finished inthe conventional manner. This finishing process can include theapplication of wicking agents, water repellents, stiffening agents,softeners, and the like. At this stage, the finished fabric normallycontains residual dye-assistant in a concentration of approximately 0.5%to 10% owf, depending on the dye-assistant used and total processing.Typically, it is preferred to keep the levels of residual dye-assistantsin the lower portion of the range, approximately between 0.5% and 5.0%owf.

Illustrative of the beneficial results attainable when dyeing at lowtemperatures as compared with dyeing at high temperatures, Table Iprovides phosphorous compound retention data for identical samples of a75/25 blend of NOMEX T-462® and FR rayon that were separately dyed at250° F. (˜121° C.) and 185° F. (85° C.). As evidenced by these testdata, much larger amounts of phosphorus compound are retained whendyeing at 185° F. as opposed to 250° F., especially after repeatedindustrial launderings conducted in accordance with NFPA 1975, 1994 ed.,s. 4-2.4 as described in the publication entitled Standard ofStation/Work Uniforms for Fire Fighters, 1994 edition, which is herebyincorporated by reference. TABLE I PHOSPHORUS RETENTION PhosphorusConcentration* Peak Dye After Launderings Dye-Assistant Temperature 0 2550 75 100 benzyl alcohol 250° F. (˜121° C.) 0.66 0.59 0.51 0.35 0.36aryl ether 250° F. (˜121° C.) 0.54 0.47 0.29 0.44 0.25 none (water) 250°F. (˜121° C.) 0.76 0.63 0.52 0.43 0.34 aryl ether 185° F. (85° C.) 0.770.70 0.64 0.65 0.61 N-cyclohexylpyrrolidone 185° F. (85° C.) 0.74 0.660.65 0.62 0.61 none (water) 185° F. (85° C.) 0.77 0.70 0.70 0.67 0.67*Phosphorus concentration was determined by inductively coupled plasma -atomic mission spectroscopy hydrochloric acid digestion of samples.

As shown in Table II, phosphorus retention is maintained when dyeingaccording to the present invention even at temperatures approaching 100°C. In group A, identical samples of a 65/35 T-462® blend of NOMEX and FRrayon were union dyed at 210° F. (˜99° C.) for 60 minutes usingN-cyclohexylpyrrolidone as a dye-assistant. In group B, the samples wereunion dyed under the same conditions but for 90 minutes at a peaktemperature of 210° F. In samples 1-4 of each group, 3g/l of AB80® wereadded to the dyebath. All samples were also laundered 100 times inaccordance with NFPA 1975, 1994 ed., s. 4-2.4. As is evident from thesedata, phosphorous concentrations stayed above 0.5% when dyed for either60 or 90 minutes regardless of whether AB80® was added to the dyebath ornot. TABLE II PHOSPHORUS RETENTION (Peak Dyeing Temp. = 210° F. (˜99°C.)) Amt. of Dye-Assistant Phosphorus Sample No. Used (g/l)Concentration (%) Group A: 60 min. peak dye time 1 30 0.82 2 35 0.82 340 0.74 4 45 0.81 5 30 0.55 6 35 0.58 7 40 0.55 8 45 0.54 Group B: 90min. peak dye time 1 30 0.77 2 35 0.80 3 40 0.84 4 45 0.78 5 30 0.65 635 0.68 7 40 0.60 8 45 0.60

Testing has shown that blends of inherently flame resistant fibers andflame resistant cellulosic fibers must have a phosphorus concentrationof at least approximately 0.5% owf to remain adequately flame resistantin accordance with FTMS 191A Method 5903.1 as described in thepublication entitled FTMS Textile Test Methods, 1978 edition, which ishereby incorporated by reference. According to Method 5903.1, a threeinch by twelve inch fabric specimen is placed in a holder and issuspended vertically over a 1½ inch high methane gas flame. During thetest, the material is placed in contact with the flame at the flame'smid-point for a period of twelve seconds. After expiration of the twelveseconds, the flame is extinguished and the material observed to, interalia, determine how long it will continue to burn. This duration ofburning after extinguishment of the methane flame is referred to as“afterflame.” Presently deemed acceptable under military and NFPAstandards are afterflame durations of 2.0 seconds and less.

Tables III and IV provided below illustrate the criticality of the 0.5%owf measure of phosphorus retention on afterflame control. The data inTable III was obtained by dyeing identical samples of 75/25 blends ofNOMEX® and FR rayon with the various listed dye-assistants at 250° F.(note that “CHP” stands for N-cyclohexylpyrrolidone and “BPP” stands foremulsified butyl/propylphthalimide). After dyeing, the samples wereindustrially laundered 0, 25, 75, or 100 times in accordance with NFPA1975, 1994 ed., s. 4-2.4, and then exposed to flame in accordance withtest method FTSM 5903.1 for three seconds instead of twelve. Althoughonly providing a three second exposure to flame, it is believed that thethree second flame exposure is a more critical indicator of fabricperformance than the twelve second exposure of FTMS 5903.1. Inparticular, the twelve second duration provides greater opportunity offlame extinguishment (see Table III). Additionally, the twelve secondflame exposure period does not reflect the fabric's resistance to flashfires which typically inflict damage primarily within the first three tofour seconds. Under the three second exposure test, afterflames greaterthan 0.8 seconds provide cause for concern in that afterflames thatexceed 0.8 seconds indicate an increased likelihood of injury to thefabric wearer. As is evident from the data of Table II, afterflamesgreater than 0.8 seconds are consistently avoided when the phosphorusconcentrations of the fabric is at least approximately 0.5% owf. TABLEIII AFTERFLAME RELATIVE TO PHOSPHORUS RETENTION (Three Second Exposure)No. of Phosphorus Afterflame Dye-Assistant Launderings Concentration (%)(sec) none (water) 0 0.76 0.1 aryl ether 0 0.54 0.8 acetophenone 0 0.590.5 CHP 0 0.69 0.5 benzyl alcohol 0 0.66 0.4 BPP 0 0.78 0.4 none (water)25 0.63 0.4 aryl ether 25 0.47 0.5 acetophenone 25 0.42 0.4 CHP 25 0.490.5 benzyl alcohol 25 0.59 0.4 BPP 25 0.35 0.4 none (water) 50 0.52 0.4aryl ether 50 0.29 3.5 acetophenone 50 0.35 0.6 CHP 50 0.38 0.6 benzylalcohol 50 0.51 0.4 BPP 50 0.42 1.1 none (water) 75 0.43 0.6 aryl ether75 0.44 0.6 acetophenone 75 0.30 29.8 CHP 75 0.39 0.6 Benzyl alcohol 750.35 1.0 BPP 75 0.44 0.9 None (water) 100 0.34 0.7 Aryl ether 100 0.254.0 Acetophenone 100 0.25 24.1 CHP 100 0.37 1.1 Benzyl alcohol 100 0.360.8 BPP 100 0.30 2.6

Table IV provides afterflame data of the same fabric and dye-assistantstested in Table II, but after twelve seconds of exposure to flame inaccordance with FTMS 5903.1. TABLE IV AFTERFLAME RELATIVE TO PHOSPHORUSRETENTION (Twelve Second Exposure) No. of Phosphorus AfterflameDye-Assistant Launderings Concentration (%) (sec) none (water) 0 0.76N/A aryl ether 0 0.54 0.0 acetophenone 0 0.59 0.0 CHP 0 0.69 0.0 benzylalcohol 0 0.68 0.0 BPP 0 0.78 0.0 none (water) 25 0.63 0.0 aryl ether 250.47 0.2 acetophenone 25 0.42 0.0 CHP 25 0.49 0.0 benzyl alcohol 25 0.590.0 BPP 25 0.35 0.0 none (water) 50 0.52 0.0 aryl ether 50 0.29 0.0acetophenone 50 0.35 0.0 CHP 50 0.38 0.0 benzyl alcohol 50 0.51 0.0 BPP50 0.42 0.0 none (water) 75 0.43 0.0 aryl ether 75 0.44 0.0 acetophenone75 0.30 16.1 CHP 75 0.39 0.0 benzyl alcohol 75 0.35 0.0 BPP 75 0.44 0.0none (water) 100 0.34 0.0 aryl ether 100 0.25 0.0 Acetophenone 100 0.2513.9 CHP 100 0.37 0.0 Benzyl alcohol 100 0.36 0.0 BPP 100 0.30 0.0

Taking into account fabric composition, it has been determined that aphosphorus compound concentration of approximately 0.5% owf translatesinto a phosphorus concentration of at least approximately 1.4%phosphorus by weight of cellulosic fiber component. In that it isdesired to have a fabric which is adequately flame resistant even afterextensive laundering, where phosphorus compound is used as the flameretardant contained in the cellulosic fibers it is preferred that theresultant blends have a phosphorus concentration of at leastapproximately 1.4% phosphorus by weight of cellulosic fiber componentafter 100 launderings conducted in accordance with NFPA 1975, 1994 ed.,s. 4-2.4.

As described above, high temperatures are typically needed and used fordyeing inherently flame resistant fibers. However, as illustrated inTable I, such high temperatures deplete the flame retardants containedin the cellulosic fibers resulting in reduced flame resistance of thefabric blend. Accordingly, the dye-assistant used must promote dyeing ofthe inherently flame resistant fibers at relatively low temperatures.With this consideration in mind, additional testing was conducted withNOMEX®/FR rayon blends at low temperature to determine the degree ofshade depth attainable when dyeing with a variety of alternativedye-assistants. Using several identical samples of a 65/35 blend ofNOMEX IIIA® and FR rayon fibers and a laboratory launderometer dyeapparatus, ten separate dyeing trials were made, each with a differentdye-assistant (see Table V). In each trial, the launderometer tube wasloaded at a 10:1 liquor ratio with the dyebath containing 2.8% basicblue dye C.I. #41 owf and 40 g/l of the particular dye-assistant beingtested (water was used as a control in the last trial). Dyeing wasconducted at 85° C. for 60 minutes. Shade depth was measured terms ofthe lightness or L value of the standardized L,a,b scale. In accordanceto this scale, the smaller the value of the L parameter, the deeper theshade, and therefore the greater the extent of dyeing achieved. Asindicated in Table V, each of N-cyclohexylpyrrolidone, benzyl alcohol,N,N-dibutylformamide, N,N-diethyl-m-toluamide, aryl ether,N-octylpyrrolidone, and N,N-dimethylbenzamide provided a deep shade ofdyeing. TABLE V SHADE DEPTH (Peak Dyeing Temp. = 85° C.) Dye-AssistantShade Depth (L) N-cyclohexylpyrrolidone 27.84 N,N-diethyl-m-toluamide28.30 *aryl ether 27.93 N-octylpyrrolidone 27.80 N,N-dibutylformamide28.22 butylbenzesulfonamide 36.20 benzyl alcohol 26.98N,N-dimethylbenzamide 29.06 sodium xylene sulfonate 36.75 water 33.85*Aryl ether dye-assistants are commercially available from Miles,Hickson Dan Chem, or Stockhausen as proprietary products.

As identified above, acceptable dyeing can be achieved with temperaturesbelow 85° C. Tables VI, VII, and VIII illustrate the depths of shadeattainable with dyeing at 50° C., 60° C., and 70° C., respectively. Ineach trial, identical samples of 100% NOMEX IIIA® were dyed with 40 g/lof the selected dye-assistant present. TABLE VI SHADE DEPTH (Peak DyeingTemp. = 50° C.) Dye-Assistant Shade Depth (L) N-cyclohexylpyrrolidone41.55 Benzyl alcohol 29.38 N,N-dibutylformamide 40.92N,N-diethyl-m-toluamide 39.04 N,N-diethylbenzamide 38.20 Acetophenone39.89

TABLE VII SHADE DEPTH (Peak Dyeing Temp. = 60° C.) Dye-Assistant ShadeDepth (L) N-cyclohexylpyrrolidone 34.68 benzyl alcohol 27.80N,N-dibutylformamide 35.84 N,N-diethyl-m-toluamide 38.69N,N-diethylbenzamide 33.83 acetophenone 31.32

TABLE VIII SHADE DEPTH (Peak Dyeing Temp. = 70° C.) Dye-Assistant ShadeDepth (L) N-cyclohexylpyrrolidone 22.62 benzyl alcohol 20.35N,N-dibutylformamide 25.42 N,N-diethyl-m-toluamide 33.45N,N-diethylbenzamide 23.42 acetophenone 21.09

In addition to permitting deep coloration of the inherently flameresistant fibers, the method of the present invention reduces theshrinkage of the inherently flame resistant fibers and therefore fabricblends containing such fibers. Table IX provides shrinkage data for65/35 blends of NOMEX IIIA® and FR rayon fibers dyed with 40 g/l ofvarious carriers at 85° C. for 60 minutes. Each fabric sample was thensubjected to 5, 10, and 20 AATCC Test Method 135-1992, TableI(3)(V)(A)(iii) launderings as described in the publication entitledAmerican Association of Textile Chemists and Colorists, 1992 edition,which is hereby incorporated by reference. As is evident from Table IX,the least amount of shrinkage occurred when the dye-assistant used wasN-cyclohexylpyrrolidone, benzyl alcohol, and N,N-dibutylformamide, withthe warp direction of the fabric only shrinking 3.8%, 5.7%, and 6.6%after 20 launderings. TABLE IX FABRIC SHRINKAGE (Peak Dyeing Temp. = 85°C.) Fill Shrinkage (%) Wrap Shrinkage (%) Dye-Assistant 5× 10× 20× 5×10× 20× N-cyclohexylpyrrolidone 1.5 2.1 2.1 3.0 3.5 3.8N,N-diethyl-m-toluamide 4.1 6.1 7.1 5.1 7.8 9.7 aryl ether 4.6 7.1 10.25.1 9.1 12.6 N,N-octylpyrrolidone 4.1 5.6 7.7 5.1 7.5 10.2N,N-dibutylformamide 2.1 3.1 3.1 3.0 4.9 5.7 butylbenzesulfonamide 6.27.7 11.8 7.5 11.2 18.7 benzyl alcohol 1.0 3.1 4.7 2.7 4.9 6.6N,N-dimethylbenzamide 4.1 7.1 9.6 6.5 9.7 12.4 sodium xylene sulfonate5.6 8.6 12.7 7.4 11.9 16.1 water 5.6 8.2 12.2 7.2 11.7 15.9

Table X provides shrinkage data for identical samples of 100% NOMEXIIIA® fabric at 70° C. for 60 minutes. After dyeing, each sample waslaundered 5, 10, and 20 times in accordance with AATCC Test Method135-1992, Table I(3)(V)(A)(iii). As shown in this table, commerciallyacceptable shrinkage control is obtainable at temperatures as low as 70°C. TABLE X FABRIC SHRINKAGE (Peak Dyeing Temp. = 70° C.) Fill Shrinkage(%) Warp Shrinkage (%) Dye-Assistant 5× 10× 20× 5× 10× 20×N-cyclohexylpyrrolidone 3.4 5.2 8.2 5.9 7.3 11.4 (30 g/l)N-cyclohexylpyrrolidone 4.1 5.2 9.3 5.2 7.5 12.4 (40 g/l) benzyl alcohol3.3 4.9 8.0 4.9 6.7 11.1 (30 g/l) benzyl alcohol 4.1 5.2 8.2 4.1 6.410.3 (40 g/l) N,N-dibutylformamide 5.7 7.7 12.9 7.2 10.1 16.0 (40 g/l)

Although the shrinkage data provided above in Tables IX and X pertainspecifically to shrinkage after dyeing the inherently flame resistantfibers, it is to be noted that the shrinkage of the inherently flameresistant fibers of these fabric blends can be controlled withoutactually dyeing the fibers. For instance, if a blend having just thecellulosic fibers dyed (or no fibers dyed) were desired, the dyeingprocess described above would be followed with the exception that dyewould not be included in the dyebath or other medium. Similarly, justthe inherently flame resistant fibers of the blend could be dyedaccording to the present method, if desired.

The results of Tables I-X illustrate that blends of inherently flameresistant fibers such as aromatic polyamides, polyamide imides, andpolyimides, and cellulosic fibers such as rayon, acetate, triacetate,and lyocell that contain a flame retardant compound can be effectivelydyed such that the inherently flame resistant fibers are dyed a fullshade of color (including deep shades, if desired), and the amount offlame retardant compound contained in the cellulosic fiberssubstantially maintained such that there is not a significant loss offlame resistance in the end fabric. Moreover, these results show thatwhere inherently flame resistant fibers are susceptible to launderingshrinkage, dyeing or shrinkage inhibiting according to the presentinvention significantly reduces such shrinkage.

In the specification and examples, there have been disclosed preferredembodiments of the invention, although specific terms are employed, theyare used in a generic and descriptive sense only and not for the purposeof limitation, the scope of the invention being defined by the following

1-2. Cancelled
 3. A method for dyeing a flame resistant fabric blend containing inherently flame resistant fibers and cellulosic fibers that contain a flame retardant compound, said method comprising: contacting a flame resistant fabric blend comprising inherently flame resistant fibers and cellulosic fibers that contain a flame retardant compound with a dyebath including at least one dye and a dye-assistant selected from the group consisting of hexadecyltrimethyl ammonium salt, N,N-diethyl-m-toluamide, aryl ether, and mixtures thereof; and heating the dyebath while in contact with the flame resistant fabric blend to fix the dye within the inherently flame resistant fibers.
 4. The method of claim 3, wherein the inherently flame resistant fibers are essentially composed of at least one of aromatic polyamide, polyamide imide and polyimide.
 5. The method of claim 3, wherein the inherently flame resistant fibers are meta-aramid fibers.
 6. The method of claim 3, wherein the cellulosic fibers are essentially composed of rayon, acetate, triacetate, lyocell, or mixtures thereof.
 7. The method of claim 3, wherein the cellulosic fibers are rayon fibers.
 8. The method of claim 3, wherein the dye assistant is hexadecyltrimethyl ammonium salt.
 9. The method of claim 3, wherein the dye assistant is N,N-diethyl-m-toluamide.
 10. The method of claim 3, wherein the dye assistant is aryl ether.
 11. A method for inhibiting laundering shrinkage in a flame resistant fabric blend containing inherently flame resistant fibers and cellulosic fibers that contain a flame retardant compound, said method comprising: contacting a flame resistant fabric blend comprising inherently flame resistant fibers and cellulosic fibers that contain a flame retardant compound with an aqueous solution containing a dye-assistant selected from the group consisting of hexadecyltrimethyl ammonium salt, N,N-diethyl-m-toluamide, aryl ether, and mixtures thereof; and heating the solution while in contact with the flame resistant fabric blend.
 12. The method of claim 11, wherein the inherently flame resistant fibers are essentially composed of at least one of aromatic polyamide, polyamide imide and polyimide.
 13. The method of claim 11, wherein the inherently flame resistant fibers are meta-aramid fibers.
 14. The method of claim 1 1, wherein the cellulosic fibers are essentially composed of rayon, acetate, triacetate, lyocell, or mixtures thereof.
 15. The method of claim 11, wherein the cellulosic fibers are rayon fibers.
 16. The method of claim 11, wherein the dye assistant is hexadecyltrimethyl ammonium salt.
 17. The method of claim 1 1, wherein the dye assistant is N,N-diethyl-m-toluamide.
 18. The method of claim 11, wherein the dye assistant is aryl ether.
 19. A method for dyeing a flame resistant fabric blend containing aramid fibers that contain a surfactant dye-assistant and cellulosic fibers that contain a flame retardant compound, said method comprising: contacting a flame resistant fabric blend comprising aramid fibers that contain a surfactant dye-assistant and cellulosic fibers that contain a flame retardant compound with a dyebath including at least one dye; and heating the dyebath while in contact with the flame resistant fabric blend to fix the dye within the aramid fibers.
 20. The method of claim 19, wherein the surfactant dye-assistant is hexadecyltrimethylammonium salt or isopropylammonium dodecylbenzenesulfonate.
 21. A method for inhibiting laundering shrinkage in a flame resistant fabric blend containing aramid fibers that contain a surfactant dye-assistant and cellulosic fibers that contain a flame retardant compound, said method comprising: contacting a flame resistant fabric blend comprising aramid fibers that contain a surfactant dye-assistant and cellulosic fibers that contain a flame retardant compound with an aqueous solution; and heating the solution while in contact with the flame resistant fabric blend.
 22. The method of claim 21, wherein the surfactant dye-assistant is hexadecyltrimethylammonium salt or isopropylammonium dodecylbenzenesulfonate.
 23. A method for dyeing a flame resistant fabric blend containing inherently flame resistant fibers and cellulosic fibers that contain a flame retardant compound, comprising: contacting a flame resistant fabric blend comprising inherently flame resistant fibers and cellulosic fibers that contain a flame retardant compound with a dyebath including at least one dye and a dye-assistant selected from the group consisting of N-cyclohexylpyrrolidone, benzyl alcohol, N,N-dibutylformamide, N,N-diethylbenzamide, hexadecyltrimethyl ammonium salt, N,N-dimethylbenzamide, N,N-diethyl-m-toluamide, N-octylpyrrolidone, aryl ether, an approximately 50/50 blend of N,N-dimethylcaprylamide and N,N-dimethylcapramide, and mixtures thereof; and heating the dyebath while in contact with the flame resistant fabric blend to fix the dye within the inherently flame resistant fibers.
 24. The method of claim 23, wherein the inherently flame resistant fibers are essentially composed at least one of aromatic polyamide, polyamide imide and polyimide.
 25. The method of claim 23, wherein the inherently flame resistant fibers are meta-aramid fibers.
 26. The method of claim 23, wherein the cellulosic fibers are essentially composed of rayon, acetate, triacetate, lyocell, or mixtures thereof.
 27. The method of claim 23, wherein the cellulosic fibers are rayon fibers.
 28. The method of claim 23, wherein the dye-assistant is selected from the group consisting of N-cyclohexylpyrrolidone, benzyl alcohol, N,N-dibutylformamide, and mixtures thereof.
 29. The method of claim 23, wherein the dye-assistant is one of N-cyclohexylpyrrolidone, benzyl alcohol, and N,N-dibutylformamide.
 30. A method for inhibiting laundering shrinkage in a flame resistant fabric blend containing inherently flame resistant fibers and cellulosic fibers that contain a flame retardant compound, comprising: contacting a flame resistant fabric blend comprising inherently flame resistant fibers and cellulosic fibers that contain a flame retardant compound with an aqueous solution containing a dye-assistant selected from the group consisting of N-cyclohexylpyrrolidone, benzyl alcohol, N,N-dibutylformamide, N,N-diethylbenzamide, hexadecyltrimethyl ammonium salt, N,N-dimethylbenzamide, N,N-diethyl-m-toluamide, N-octylpyrrolidone, aryl ether, an approximately 50/50 blend of N,N-dimethylcaprylamide and N,N-dimethylcapramide, and mixtures thereof; and heating the solution while in contact with the flame resistant fabric blend.
 31. The method of claim 30, wherein the inherently flame resistant fibers are essentially composed of at least one of aromatic polyamide, polyamide imide and polyimide.
 32. The method of claim 30, wherein the inherently flame resistant fibers are meta-aramid fibers.
 33. The method of claim 30, wherein the cellulosic fibers are essentially composed of rayon, acetate, triacetate, lyocell, or mixtures thereof.
 34. The method of claim 30, wherein the cellulosic fibers are rayon fibers.
 35. The method of claim 30, wherein the dye-assistant is selected from the group consisting of N-cyclohexylpyrrolidone, benzyl alcohol, N,N-dibutylformamide, and mixtures thereof.
 36. The method of claim 30, wherein the dye-assistant is one of N-cyclohexylpyrrolidone, benzyl alcohol, and N,N-dibutylformamide. 